Process of making castings of rare-earth metals and their alloys.



A. I M. HIRSCH. PROCESS 0E MAAING CASTINGS 0E RARE EARTH METALS ANOTHEIR ALLoYS.

APPLICATION FILED VIAY9-19l8.

Patented Dec. 3l, 1916.

UNITED STATES PATENT OFFICE.

ALCAN HIRSCH AND MARX HIRSCH, OF NEW YORK, N. Y., ASSIGNORS T0 ALPHAPRODUCTS COMPANY, INC., A CORPORATION 0F NEW YORK.

PROCESS 0F MAKING CASTINGS OF BABE-EARTH METALS AND THEIR ALLOYS.

Specification of Letters Patent.

Patented Dec. 31, 1918.

Original application tiled September 17, 1917, Serial No. 191,868.Ilivided and this application illed May 9, 1918. Serial No. 233,452.

To all whom t may concern Be it known that we, ALCAN HIRSCH and M ARXHmscu, citizens of the United States, and residents of New York, in thecounty of N ew York and State of New York, have invented certain new anduseful Improvements in Processes of Making Castings of Rare- EarthMetals and Their Alloys, of which the following is a specification.

The invention relates to improvements in the manufacture of castings ofrare earth metals and their alloys. The improvements are particularlyadapted t0 the manufacture of castings of alloys of cerium or lanthanumfor sparking purposes. This application is a division of our priorapplication Serial No. 191663 filed September 17, 1917.

Prior to the present invention it has been considered extremelydifficult to cast the desired rods and shapes of cerium and its alloyshaving a very small cross section and volume with respect to surface,because of the extreme inflammability of the metal on the one hand andits great tendency to chemical reaction with carbon and other substancesand to alloyinfg` with metals on the other hand. It was only by thelaborious and wasteful process of sawing or turning beneath the surfaceof oil, or while constantly drenching the fresh surfaces and cuttingswith oil, that it was generally known how to make the small commercialshapes necessary for use in lighters, ignition flints, etc.

The present process` has for its object the providing of improvementswhereby the rare earth metals and their alloys may be satisfaetorilycast in the various forms desired in commerce and, in many cases, withSullicient eXact1tude of size to avoid the necess1ty of machining,thereby avoiding not only delay and expense, but much loss of material,which, once powdered. is extremely diflicult to recover in usable shape.Also, according to the present invention, the cast metal or alloy isobtained in a most simple and economical manner and substantially freefrom objectionable impurities.

Further and more specific objects, features and advantages will moreclearly appear from the detailed description given below taken inconnection with the accompanying sheet of drawings, which forms a partof this specification.

In the drawing,

Figure l is a vertical -section of a preferred form of apparatus formelting the metals;

Fig. 2 is a top view of a mold into which the molten metal may bepouredfor castin g Fig. 3 is a vertical section taken on t e line 3 3 of Fig.25

Fig. 4 is a vert1cal section taken on the line 4-4 of Fig. 2;

Fig. 5 is a top planview illustrating a modified form of mold; and

Fig. 6 1s a similar view illustrating still another form of mold.

As an illustrative example of the improvements, the preferred processfor the manufacture of castings of an allo of cerium, lanthanum,didymium, etc., an iron will be described.

Large pigs of an alloy of cerium, lauthanum and didymium, and possiblysmall quantities of erbium and thorium, etc., and containing more orless impurities are broken up, as with a hammer, into pieces about oneinch diameter. It is preferred to avoid using much smaller pieces thanone-half inch in diameter, as they tend to thicken the melt into whichthey are later put, probably because of the greater amount of oxidformed on the surfaces of the pieces when an equal weight of smallerpieces is used. Larger pieces may be used, especially in the largermelts.

Into a suitable cl'ucible, preferably a Hessian or Battersea Crucible,and suitably heated, a quantity of barium chlorid crystals is put in andmelted down. For this purpose, an apparatus such as shown in Fig. l maybe used, in which l represents the crucible,

2 a supporting bed portion of fire-brick, pro-y barium chlorid crystalshas been evolved and the mass reached a quiet state of fusion, thepieces of metal, consisting mostly of cerium with some lanthanum andsmall quantities of other metals, are Washed in kerosene or othersuitable oil to remove dirt, oxids and carbids thatl may be on thesurface thereof, and then they are partially dried, as with news printpaper, and then' the piecesof metal are added to the melt of bari rr.chlorid in fairly large batches, that is to say, as many pieces areadded at a-time as can be readily shoved under the surface of the bariumchlorid. Any kerosene or other oil remaining on the pieces burns off asthey go into the molten barium chlorid. The mass should not he stirred,and in adding the metal the melt should be agitated as little aspossible. The cerium metal or alloy added should preferably be low iniron, as metal high in iron notV only has a higher melting point, but isapt to contain more of other impurities and these impurities are thenfar more diflicult to separate. prefer to use a rare earth metalcontaining about 10% or less of iron. Nhen the metal added has becomefluid at the bottom of the crucible, another batch of metal may be addedin the same Way and the molten metal batch built up, care being takennot to expose the already molten cerium metal in the melt to the air,which Would rapidly ignite or oxidize it. The heatin of the pieces ofmetal to melt them shou d be carried out relatively quickly, because, ifthe operation is carried out slowly, the metal melt does not become asclear and homogeneous, the fused salt above it becomes more viscous andditlicut to separate from the metal, and much metal is apt to be lost,nor does the metal pour so Well when it is later poured from thecrucible. By relatively quickly We mean that the Whole operation ofmelting, alloying and casting the metal should take not over about twohours, instead of several hours.

When the crucible is about one-half full of molten metal, as illustratedat 6 in Fig. 1, any other metal which it is desired to alloy With it isadded. In most cases, it is desirable -to add certain other metals, suchas iron, to harden the resulting alloy. This is added in the form ofsoft wrought iron Wire. It is first cut olf in pieces Weighing, say, 40to 50 grams and the pieces wound into loose coils or spools. These coilsof Wire are poked into the melt under the layer 7 of barium chlorid. Ifiron alone is used, it is preferred to add sufficient iron so that theresulting alloy contains about 30% of iron. The iron is preferably addedperiodically in about four batches. The iron becomes hot in the bath andalloys with tlie molten cerium, etc. The layer of barium chloridprevents oxidation of both metals. If there is We, therefore,

meadow not sucient barium chloridvin the crucible so that portions ofthe iron Wire protrude, these portions are covered with some bariumchlorid to prevent oxidation and the heating continued until they areall melted into the alloy. Before the addition of any subsequent bath ofiron, the previous batch of iron should be thoroughly absorbed. Duringthe additi^n of the iron, care should be takennot to stir the batch anymore than is absolutely necessary. When all the iron or other metal isadded, the temperature may be raised to about 10000 C. which increasesthe Y fluidity of the molten metal. When the melt is fairly liquid, andabout ten minutes before it is poured out., it is thoroughly but gentlystirred to lproduce a homogeneous mass. It is important to increase thefluidity in order that, vvhen stirred it shall be thoroughly mixed, .andWhen poured into the molds the molten metal Will be suiciently iuid notto be congealed prematurely as more clearly pointed out hereinafter. Anadditional layer of barium chlorid may be added, if necessary.

TWhen the metal is thoroughly molten and homogeneous, the crucible islifted out of the furnace and a hole poked through the crust, if any, ofbarium chlorid adjacent the side of the crucible, by means of a hot ironbar or rod. The molten metal is then poured through this hole out intosuitable molds. lt is desirable to make up melts of metal of over 350grams, preferably about 2-3 kilograms, as, if smaller melts, say of 200grams, are used, difficulty is encountered in pouring the metal.

While any form of molds may be used, it is preferred to maire them ofiron or have the casting face of iron or the like. However, graphite andother materials may be used for the molds. The mold, especially if madeof solid iron, should he uniformly heated to about 400 C. It should beover 100o C. This heating of the mold permits the pouring of the metalat a temperature so near to the solidifying point that excessive burningis avoided and at the same time permits this metal, near to the point ofcongelation, to find its way into and lill the mold. The mold should beslowly and uniformly heated to prevent warping thereof. By thus heatingthe metal mold the residual heat absorbing capacity of the-mold, up tothe temperature of congelation of the molten metal is reduced to a pointWhere it does not materially affect the homogeneity of the resultingcasting by causing cracks, breaks, strings and cold shots and similarimperfections in the casting, caused by rapid and uneven cooling of themolten metal. This may be accomplished in other Ways. Instead of heatinga heavy metal mold' a thin sheetmetalmold having little heat absorbingcapacity may be used to accomplish the same result. In Figs. 2, 3 and 4there is illustrated an iron mold composed of two parts 10 and 11, thepart 10 being a dat iron plate, and the part 11 being a flat iron plate,provided wlth grooves 12, extendlng from the top nearly to the bottomthereof. A connecting groove 13 is provlded at the top. The plates maybe held together by four angle bars 14 running along near the top andbottom on the outside of the plates and pulled together by bolts 15. Theresulting castings have an unusually small dlameter or 'cross sectionand relatively great length and the ratio ofthe area in square inches ofthe molding surface from which withdrawal of heat may take place, to thevolume in cubic inches of the casting to be produced, is greater than 16to 1. In order that this relatively large heat withdrawal surface maynot cause premature congelation in the mold of the metal, already nearthe point of congelation, and prevent the complete How of molten metalnear the temperature of incipient congelation, into the mold, thechilling capacity of the mold is reduced as above described, and thefluidity of the molten metal is increased prior to pouring, by stirringand by a slight increase in the temperature thereof, as above described,to permit the molten metal to penetrate the mold cavities withsubstantial completeness before the stage of incipient congelation ispassed.

Before pouring the metal into the mold, the surfaces of the mold may bedusted or otherwise coated with a layer of magnesia or other inertmaterial such as rolling scale or tin plating, so that the pieces ofcast metal may be easily removed from the mold. The metal is poured intothe connecting slot 13 and runs into the mold slots 12, filling them up.The mold should be allowed to cool slowly, that is, no artificial meansare used to hasten the cooling, but the mold is allowed to air cool, sothat it cools with suilicient rapidity to prevent any substantialoxidation .of the metal. If the coating of inagnesia has been uniform, aslight tapping of the plate 11, after plate 10 has been removedtherefrom,should so loosen the pieces of cast metal that they may beeasily removed.

In Fig. 5 is shown a top view of a similar mold adapted to formcylindricalshaped castings or sticks of metal, and in Fig. 6 is shown avtop view of a similar mold adapted to cast sticks of metal rectangularin crosssection.

The resulting cast sticks of metal as they come from the molds shown inFigs. 2 to 6 are especially adapted for sparkingv purposes and differmaterially from the pieces of alloy heretofore used for this purpose andwhich were made by sawing or turning under oil. The alloy castings madeaccording to our process, have matt unsmeared glassy sur faces whereformed adjacent the metal mold surface. While the surfaces may besomewhat rough owing to the presence of some air or blow holes on thesurface, yet the surfaces have a characteristic glassy appearance andthe metal is not smeared over as is the case when the pieces are formedby sawing or turning. Moreover, especially when cast in the metal molds,it is found that the castings at said surfaces have a superficial skinpartly composed of the alloy, but poorer in the rare earth metal than isthe alloy in the interior of the cast piece. This probably is due to thealloyV taking up metal or particles from the metal mold surface. Thisskin serves as a substantially non-corrosive coating or layer while thenecessary sparking roperties are not interfered with thereby.

y melting and pouring the alloyed metals from beneath a fused salt asabove described, flakes of oxid, which would otherwise be present. inthe casting, are substantially eliminated and theresultant casting isextremely homogeneous.

In many cases. it is found that crude metal (chiciiv cerium orlanthanum). as taken from the. electrolytic cell in which it isproduced, is so impure or non-homogeneous that a stable and sufficientlyair-resistant alloy is not produced by a `single fusion of the crudemetal under the purifying bath.

as of barium chlorid. In such case, it is desirable to make two or moresuccessive fusions as described. preferably before alloying (raising themelting point) and casting into final shapes (separating the metal oralloy into small pieces). After each such preliminary purifying fusion,the slagr or fused salt may be removed from the crucible and freshpurifying salt already dehydrated -added to the metal therein, or themetal may be cast into pigs of convenient size (about 1X1x4 inches) forremolding or for breaking into lumps for remelting.

While it has been suggested that in the making of certain brass, bronzeand steel alloys, themetal may be melted below a laver of boraX orWaterglass. this a very different proposition from the making ofcastings of the rare earth metals, such as cerium or lanthanum` andtheir pyrophoric alloys which congeal readily and pour with diiicultynear their congealing point.. Cerium is not only readily oxidized whenheated. but rapidly ignites, and, furthermore` has such a great affinityfor oxygen that if melted below such glass as borax or waterglass, wouldso rapidly combine with the oxygen therein as to cause a violentreaction. With the brass, bronze and steel alloys. there is no suchproblem. The making of bronze, brass and steel castings is an artdistinct and separate from the art of making castings and suitable forcommercial use from pyrophoric alloys of cerium and similar rare earthmetals in which the active that they earhen iorni @are num under acovering layer of sodium chlothe Working temperature.

,sponding loss of the salt,

' Other methods rid and potassium chlorid, but unless certain additionalfeatures or precautions are employed in the process, the results are verunsatisfactory and even then barium chlorid has distinct advantages notpossessed by a mixture of sodium chlorid and potassium chlorid.

Instead of using barium chlorid as a protecting layer for the moltenmetal, sodium chlorid and other salts inert to the rare earth metalbeing used, may be used which would prevent oxidation of the metal, butbarium chlorid has advantages over certain othe` salts, because of itsless volatility at If more volatile not only a carrebut greatinconvenience to the Workmen results. Furthermore, it-is believed tlatthe surface tension of fused cerium and its alloys against a molten bathhigh in barium chlorid is farmore advantageous to making homogeneous4castings and protectingthe surface of the metal from too rapidoxidation. Copper or magnesium may alsobe added to the molten metal ltoharden the resulting alloy, or increase the fatness and heat of thespark. preventing oxidation of the melt may be used as by carrying outthe fusion in an atmosphere of hydrogen.,

Many other changes and modifications may be made without departing fromthe spirit and scope of the invention in its broader aspects.

What is claimed as new and desired to he secured by Letters Patent isr 1. In the process of making castings of cerium and similar rare earthmetals and their alleys, the steps which consist in melting the rareearth metal and pouring it into molds, the temperature of the metal whenpoured being sucien-tly close to the congelation temperature to preventinflammation of the metal.

2. In the process of making casting of cerium and similar rare earthmetals and their alloys, the step which consists in pouring the moltenrare earth metal or alloy thereof into a mold with a metal moldingsurface in which the ratio of the area in square inches, of the moldingsurface from which Withdrawal of heat may take place,

salts are used, there is to the volume in cubic inches of the castingproduced, is greater than 16 to 1, the residual heat absorbing capacityof the" mold, up to the temperature of congelation of the molten metal,being reduced to a point where it-does not4 materially affect thehomogeneity assenze 4. In the process of making castings of .alloys ofceriumor lanthanum the steps which consist in melting rare earth metalcontaining mainly cerium or lanthannm andA protecting the molten metalfrom oxidation and pouring the molten metal into. molds andallowingfthemolds to cool slowly as at room temperature, the residualheat absorblng capacity of the mold, up to the` tempery ature ofcongelation of the molten metal, being reduced to a po'int where itdoesnot materially affect the homogeneity of the r'esulting castings byimperfections in the castrapid and unevenA cooling of' ing caused by themolten metal. K 5. In the process` of making castings of cerium andsimilar rare earth metals andV alleys thereof, the stepsA which consistin melt-ing therare earth metal or alloy thereof while protecting themolten metal from oxidation, pouring the molten metal into molds, thetemperature of the metal when poured being 'suiliciently close to thecongelation temperature to prevent inflammation of the rare earth metal,and permittinl the metal to cool inthe mold, with suicient rapidity toprevent Jany substantial oxidation thereof. Y

6. In the process of making castings of cerium and similar rare earthmetals and their alloys the steps which consist in melting the rareearth metal and pouring the molten metal into molds heated to about 100C. or over. Y

7. In the process of makin castings of cerium and similar rare eartllymetals and their alloys the steps which consist in melting the rareearth metal and pouring the moltenV metal into molds heated to about 100C. or over, and allowing the molds to' cool slowly as to roomtemperature, the molds being coated with nely divided inert material torender the cast metal more easily removable therefrom.

8.` In the proce of making castings of cerium and similar rare earthmetals and their alloys the steps which consist in melting a rare earthmetal lWhile protecting the molten metal from oxidation, and pouring themolten metal into molds, the Whole 0peration taking about two hours orless, the residual heat absorbing capacity oi' the mold, up to thetemperature of congelation of the molten metal, being reduced to a pintwhere it dees not materially aect the homogeneity of the resultingcastings by perfections in the `casting caused by-rapid and unevencooling of the molten metal.

9. In the process of making castings of cerium or similar rare earthmetals or alloys thereof the steps which consist in melting rare earthmetal containingl mainly' cerium or lanthanum and containing about 10%or less of iron, and then melting therewith an alloying metal to hardenthe resulting alloy,

and pouring the molten rare earth metal or alloy thereof into a'moldwith a metal molding surface in which the ratio of the area in squareinches, of the molding surface from which withdrawal of heat may takeplace2 to the volume in cubic inches, of the casting produced is greaterthan 16 to 1, the residual eat absorbing capacity of the mold, up to thetemperature ofcon lation of the molten metal, being reduce Ato a pointwhere it does not materiallyaffect the homogeneity of the resultingcasting by imperfectlons in the casting caused 'by rapid and `unevencooling of lthe molten metal. 10. In the proces of makmgcastn of ceriumor similar rare earth metals or a loys -thereof thesteps which consistin melting a point where it does not materially affect the homogeneityof the resulting casting by imperfections in the casting caused by rapidand uneven cooling of the moltenmetal.

L1. In the process of manufacturing castings of rare earth metal alloysthe steps which consist in pouring the molten alloy, at Ja temperaturenear the temperature of incipient congelation thereof, into multiplemolds, the mold cavities of which have a ,surface to volume ratiomeasured in square inches and cubic inches respectively, greater than 16to 1; and reducing the heat abstract' lng capacity of the moldingsurface to such` a point that the molten metal penetrates the moldcavitiesgvith substantial completeness before the stage of incipientcongelation is passed.

12. In the process of manufacturing castings of cerium and similar rareearth metals or their alloys, the steps which consist in melting` t erare earth metal or alloy and pouring t e 4molten metal into moldsresidual heat;` absorbing capacity of which,

Y up to the temperature of congelation of the molten metal, i s` reducedto a point where it does not affect the homogeneity of the resultingcasting by imperfections in the cast- 'ng caused by rapid and unevencooling of the molten metal and permitting the metal to cool in the moldwith sufficient rapidity to prevent any substantial oxidation thereof.

Signed at New York, in the county-of New York -andState of New York,this 6th day of May, A. D. 1918.

ALGAN HIRsoH. Y MARX HIRsoH.

Witnesses y Je R. BAILEY,

the A

